Cathode



Oct. 20, 1936..

' S. H. STUPAKO FF CATHODE Filed Aug. 7, 1930 INVENTOR Patented Oct. 20, 1936 U N'ITED PATENT o FFi cE 2,057,931 cA'rHoDE *Sem'on H. Stupakofi, Pittsburgh, Pa. .A-pplication August 7, 1930, SerialTNo. 47.3,l26

' 2 Claims. (Cl. 250--27.)

This invention relates to icathode discharge. .de- 'viceszand :morepparticularly devices of this nature having anindirecitly heated .cathodeandis for an improvement in the heating :element for such :structures.

Indirectly heated cathodes. are commonly em ployed in radio 'receiving tubes energized from Ihouse-lightingcircuits. These cathodes common- :ly comprise .a .metal cylinder :within which is supported a filamentpeither .of the hairpin type, -or non-inductively wound coil. Ineither case the filament is generally supported on a porcelain rod coextensive with the length of atheametal cylinder.

The overall permissible length of these fila .mentsis approximately onexinch. They are designed to operate on 2 volts and from 1 to 2 .amperes in the "ordinary receiving tube. It is obvious .that thediameter of the filament must be very small in order that it may have the requisite resistance, measuring around 1.2 ohms, because 'of the limited maximum length which it may have. 1

This very small filament has to maintain the emitting-element, which is the nickel cylinder, at :an operating temperature, and to "do so it must not only-heat up the nickel, but theceramic mass within the nickel cylinder on which the filament 'is supported. .It is therefore necessary to operate the filament at extremely high temperatures, approximately 2000 degreesQ, in order to maintain the-nickel cylinder, which has :a verymuch larger radiating surface, at the proper emitting temperature.

This very delicate filament must not only be handled very carefully inthe manufacture of the tube, but .at the high temperature at which it is operated it deteriorates =quite rapidly, thus imposing a considerable limitationon the active life of a tube. Another objection to this structure is that a considerable period of time, from to 45 seconds, is :required before the entire mass of the cathode becomes heated sufiiciently to cause the tube to function.

According to the present invention there is provided a form of heater or filament wherein the mass of the filament is greatly increased over that in the present forms, the mass of the filament in fact approaching that of the nickel cylinder itself. With this filament a smaller mass of ceramic insulation is required so that the total mass to be heated is considerably less. The invention therefore permits the filament to be operated at a considerably lower temperature and at the same time bring the cathode up to an operating temperature almost instantaneously. Being much less fragile :than the present filament, the construction materially.simplifies'lthe 'process .of :manufacturing and assembli-ngland reduces the cost.

The invention may be readily understood by reference to the accompanying drawing which i is :provided merely .for the purpose of illustration and to i'th'e details .of construction of which the invention is .not confined, the drawing being :on :a very much enlarged scale as compared with the actualsizerof the respective-.elementsin:an or- "dinary radio :receiving'tube.

In :thedrawing,

Figure :1 is a vertical section through that portion of a cathode with which vtheipresentinvention is concerned showing the cathode assembly,

Figure 2 is a transverse section in substantially the plane of line II-II.Of Rig. 1, V

Figure 3 is .a plan viewshowing one step .in the development of the heater,

Figure 4 'isa perspective viewss'howing the heaterain a further stage-of development,

- .ili'igure 5 is a view similar ato :Fig. 3 of aarslightly modified arrangement,

a .Figure 6 isazside elevation "of .a heater formed upfrom the element shown in Fig. 5; and

Figure 7 is aperspective View showinganother ,way of forming the :heater.

Referring to Fig. 1, 2 designates a metal cylinder,.such as the emitting elementcommonly provided in radiotubes. .At :the .topof the-cylinder is a disc orcap3 .of insulating material, this cap having -a projection 4 :on the inner surface thereof. .At the opposite end .of the cathode '2 is a second insulator -5 havingacentral opening through which the'heater :is received. The heater itself 3 is designated 6. 'It isinthe form of a cylinder of .metal :having vertically extending convolutions forming a continuous ribbon of metal and having .upwardly and downwardly extending reaches which-are separated from each other.

The construction of the heater may be "readily seen by reference to Fig. 43 which illustrates a flat development of the heater, or shows the shape of the fiat plate from which the cylindrical heater is formed. Figure 3 discloses a flat piece of material from which the filament is formed, preferably metal, in which are cut alternately directed slots 1 and 8, the slots being of equal length and of slightly less length than the length of the metal sheet itself. By reason of this arrangement there is provided a continuous flat ribicon of metal having parallel lengths connected at one end to one adjacent length of metal and connected at the other end to the other adjacent length of metal. This sinusoidally arranged ribbon is then bent up into cylindrical form, as shown in Fig. 4. Those portions of the metal which form the opposite ends of the heater construction are preferably longer than the length of the remainder of the structure so as to provide for the connection of lead wires thereto. These extensions are designated 9 in Figs. 3 and 4. It will be noted in Fig. 4 that the extensions 9 lie adjacent to each other. In order that they may be at diametrically opposite points on the cylinder, the fiat sheet from which the cylinder is developed may be cut in the manner shown in Fig. 5. In this view it will be seen that one reach of the metal, ll, having the terminal extension I2, is at the outer edge of the strip, whereas the other reach l3 having the terminal extension I is at the middle of the strip. The convolutions are so stamped, however, as to provide a continuous ribbon of metal from the extension I2 to the extension I4 without any intermediate point of contact. When the sheet shown in Fig. 5 is rolled into cylindrical form the extensions l2 and M are diametrically opposite.

In order to facilitate the assembly of the tube, one end of the heater may be expanded or flared as shown at I5 in Figs. 1 and 6 to embrace the projection 4 and thus provide for the centering of the upper end of the heater on the projection 4 of the insulator 3. The lower end of the roller is centered by the insulator 5. By flaring portions of the lower end of the heater outwardly, as shown in Fig. 1, the insulator 5 can be retained in place. The lead wires, not shown, are connected to the heater and hold the heater against vertical displacement.

Instead of forming the heater from a flat piece of metal stamped as shown in Figs. 3 or 5, a similar construction can be obtained by cutting oppositely extending slots into a small metal tube, as illustrated in Fig. 7 wherein l6 designates a small metal tube and I1 designates the lines along which this tube may be cut to provide a ribbon-like cylindrical member.

It will be appreciated that the drawing is intended to illustrate the principle of my invention and are out of all proportion to the actual size of the parts as provided, for instance, in a small receiving tube.

The structure, by reason of the alternately reversed reaches, is substantially non-inductive due to the fact that the field set up about one reach is opposed to the field set up by the current flowing in the adjacent reaches or parallel stretches of metal. This is a desirable feature in that it minimizes or eliminates any alternating current hum or ripple in the output of the tube. Due to the number of parallel extensions of metal in the structure the actual length of the metal ribbon is many times that procurable in the present structures. Consequently, the requisite amount of heat can be obtained with the filament operating at a lower temperature.

The structure possesses considerable rigidity, being formed from fiat sheet metal bent into cylindrical shape. The mass of insulation required in the structure is relatively small, and this insulation is concentrated at the ends of the cathode structure so as not to obstruct the direct radiation of heat from the heater to the cathode 2. Thus the tube will very quickly heat to an operating temperature as compared with present tubes where there is a relatively large mass of inert material in comparison to the actual diameter of the filament. Due to the fact that the heater is larger in cross-section than the filament and can be operated at a lower temperature, the length of life of a tube employing it will be tremendously increased. The heater furthermore eliminates many of the manufacturing difiiculties encountered with the use of the present types of heaters.

The construction herein described and illustrated, while being preferable, is subject to minor modifications, for example, the filament need not necessarily be cylindrical; the tube may be centered without a flare although the flare aids in centering the tube; instead of a flare the lugs may be bent inwardly and a suitable insulator provided whereby the heater may be held in suspension while being centered; and the slotted sheet need not be bent into cylindrical form, but may be bent into U-shape and held in place in a cathode sleeve of oval or rectangular crosssection.

While I have described certain detailed embodiments of my invention and the method of forming the heater, it will be understood that this is by way of illustration, and that changes in modification may be made therein within the contemplation of my invention and under the scope of the following claims.

I claim:

1. A cathode assembly comprising an outer metal shell constituting a cathode, an inner substantially cylindrical member formed of a sinuously extending ribbon of conducting material constituting a heater, and spaced insulators at opposite ends of the cathode for supporting the heater and having the intermediate portion of the heater directly exposed to the interior of the cathode.

2. A cathode assembly comprising an outer metal shell constituting a cathode. an inner substantially cylindrical member formed of a sinuously extending ribbon of conducting material constituting a heater, an insulator at one end of the cathode having an inwardly extending projection about which one end of the heater is centered, and an insulator at the other end of the cathode having a central opening through which the heater passes.

SEMON H. STUPAKOFF. 

